In the 1940s, Flor proposed the now classic gene-for-gene model to explain the molecular basis of a plant's resistance to a bacterial pathogen. In short, this model suggests that in order for a plant to be resistant to a given pathogen, both genes, avr and R, must be present. The simplest explanation for this interaction is the receptor-ligand model, whereby the resistance gene products (R proteins) recognize, either directly or indirectly, the ligands specified by the bacterial avirulence gene products. Recognition of the ligand by the receptor is thought to initiate a signal transduction cascade leading to the activation of a variety of local and systemic defense responses. NDR1 of Arabidopsis is required for the activity of several CC/NBS/LRR resistance genes, and over-expression of NDR1 provides a dose-dependent enhanced bacterial resistance. Computer analyses suggest that NDR 1 may be a GPI-anchored protein, and as such, may be plasma membrane-localized. Localization at the plasma membrane would place NDR1 in intimate contact with the bacteria-plant cell interface. The goal of this project is to utilize a combination of genetic and biochemical approaches to identify the role NDR1 plays in the pathogen-induced defense response in Arabidopsis. [unreadable] [unreadable]